Apparatus for reproducing, amplifying, and projecting sound waves



Sept. 15, 1925.

E. GRISSINGER APPARATUS FOR RETBUDUCING, AMPLIFYING,- AND PROJECTING SOUND WAVES Filed May 11, 1920 3 Sheets-Sheet 1 Sept. 15. 1925.

' E. GRISSINGER AMPLIFYING AND PROJECTING SOUND WAVES vAPPARATUS FOR REPRODUCI NG 3 Sheets-Sheet 2 Filed May 11, 1920 Sept. 15. 1925. E. GRISSINGER APPARATUS FOR REPRODUCING, AMPLIFYI'NG, AND PROJECTING soumn WAVES 3 Sheets-Sheet 3 Filed May 11, 1920 I amvmtoz @513 Gwen mug I a Patented Sept. 15, 1925.

UNITED STATES EL'WOOD GRISSINGER, OF BUFFALO, NEW YORK.

APPARATUS FOR REPRODUCIN G, AMPLIFYING, .ALN'D PROJECTING SOUND WAVES.

Application filed May 11,

To all whom it may concern:

Be it know that I, ELwooD GRISSINGER, a citizen of the United States, and resident of Buffalo, in the county of Erie and State of New York, have invented certain, new and useful Improvements in Apparatus for Reproducing, Amplifying, and Projecting Sound Waves, of which the following is a specification.

My present invention includes a new feature which concerns the reproducing process as a whole, starting with the stylus needle, lever and diaphragm which vibrate the air in the sound box, and including propagation of the sound waves into, through and out of the tone arm and amplifying projector into the open air. It includes utilizing a reproducer having certain qualities explained in myPatents. Numbers 1,339,648; 1,339,649; and 1,339,558, in combination with a sound projector having specialqualities attainable most readily by employing a reflecting amplifier and projector of the type disclosed in my prior applications Serial Nos. 298,846

' and 305,601, preferably one with the sonorous plate reflectors arranged as shown in Figure 2 of said latter application, but preferably with certain modifications and improvements decribed hereafter.

It is characteristic of the reproducersof said applications that the levers are of rigid construction, are pivoted for movement about a rigidly fixed axis, and are associated with spring elements (wires) so arranged that although the spring tension of said elements is considerable, they afford but slight resilient opposition to oscillatory movements of the lever. lVhen such a lever so mounted is associated with a diaphragm of suitable size and sufliciently flexible the vibratory system as a whole has a low free period of natural vibration.

I have discovered that reproducers having a low free period, that is lower than the average of speech frequencies, have not here tofore come into general commercial use although they reproduce sounds with a much smoother and. more musical'quality than the Victor, Columbia, Edison and other standard commercial rcproducers. The reason for this seems to be that the present day art was developed mainly by accepting Victor 7 quality as standard and it is characteristic of Victor reproduction that the reproducer is constructed and adjusted to have a high 1920. Serial No. 380,492.

free period whereby the quality of the reproduced sound has a noticeably shrill or brilliant quality. Originally this reproducer was used in connection with the oldfashioned conical brass horn which contributed a further brilliant effect to the quality of the reproduction. Conse uently, when the trade began to pay attentlon to quality, it became the practice to mellow and dull the metallic brilliancy of the reproduction by the use of long,.low-frequency, wooden projectors, as variously embodied in phonographs of the cabinet type. The modified quality of re roduction afforded by this combination 0 high frequency, brilliant reproducer with voluminous, low-frequency projector became in turn a well-known and generally accepted standard for reproduction. The result of using a low free period reproducer in combination with such a long low frequency projector, is to muffle the sound and make it seem to originate at a remote; point, far back in the projector. I have further discovered that where the low free period reproducer is.combined with a relatively short, high frequency projector, particularly where the projection of the sound is by reflection in accordance with the principles explained in my said prior applications, the smooth quality and the perfect reproduction of overtones characteristic of such low free period reproducers, is combined with a louder more brilliant effect and appears to originate from a point in advance of the mouth of the projector instead of somewhere way be ck in the depths thereof.

My invention also includes certain improvements in the sonorous reflecting projectors which are particularly adapted for employment in combination with low frequency reproducers, though they may be also used in connection with the ordinary standard reproducers 'now on the market. As described in my prior application, the consonant reflecting plate preferably consists of a sheet or thin plate of sound sensitive material such as the wood used for piano sounding boards, rigidly secured to a rigid frame around the entire periphery of the plate. As contrasted with this, my present invention involves clamping the plates to the frames at two opposite edges and slightly recessing the frame beneath the other two opposite edges so as to leave these edges of the plate perfectly free for vibration of maximum attainable amplitude, without danger of contacting with anything. The latter construction has very important advantages. The plate can be arranged with its clamped insensitive edges joining the side walls so that only the free vibratory edges extend crosswise in the path of the waves to be reflected, thus niaking the active reflecting area uniformly elastic lengthwise of the projector instead of having it crossed by non-vibratory clamped zones which are unavoidable where the crosswise edges of the plates are clamped as in my prior devices of this type. In the case of plates formedwith diverging sides the tendency to omniperiodic resonant reenforcement of the sound is improved because there is less constraint on the plate and it can vibrate more like a set of parallel strings.

Also, a given plate of given thickness, clamped only at two opposite edges, is much more flexible and sensitive and has a lower natural frequency than when clamped about its entire periphery. Hence, plates of minimum permissible thinness may be mounted so as to be more sensitive; also in selecting plates so as to get a desired range of frequencies, or to get a desired ratio between the wave reflecting quality and the wave absorbtive and reradiating quality, the plate can be thicker and more substantial than would otherwise be possible.

Moreover, a plate clamped about its entire periphery tends to act somewhat like a diaphragm with reference to its overtone or segmental vibrations, that. is to say, its segmental vibrationsare not harmonics of its fundamental but are discordant with said fundamental and with each other. Vhen the plates are clamped only at two opposite edges, however their segmental vibrations tend to follow more nearly the harmonic law characteristic 'of stretched strings, that is to say, when vibrated by a note corresponding to one of their natural frequencies either fundamental or harmonic. the other natural frequencies excited thereby are harmonious and pleasing instead of discordant.

By proper coordination of the various features of my invention so as to take full advantage of my above described discoveries, sound effects are attainable which are entirely unique as to the loudness, vividness and perfect 'quality of the reproduced sounds.

From the above explanation, it will be evident that in its broader aspect, my invention consists of combining a reproducer of low free period with a relatively short or high frequency projector and as a preferable embodiment, emitting the sound by reflection, preferably from plates affording a desired degree of consonant re-enforcement.

The above and other features of my invention may be more fully understood from the following description of an illustrative embodiment thereof shown in the accompanying drawings, in which Figure 1 is a vertical section of a phonograph cabinet of ordinary construction liav' tion having my improved apparatus embodied therein;

Figure 2 is a detail plan view partly in section on the line 22, Figure 1;

Figure 3 is a front elevation of the projector looking into the mouth thereof, the cabinet being broken away to show the construction more clearly;

Figure 4 is a detail perspective of one of the sonorous plate elements with a portion of the plate broken away to show the frame more clearly;

Figure 5 is a detail view showing a corner joint'where a sonorous plate element and its frame are secured to the side wall of the projector;

Figure 6 is a vertical section of a projector like Figure 1 with an added feature, the section being indicated bythe. line 6'-6, on Figure 7; i

Figure 7 is a horizontal section on the line 77, Figure 6; and

Figure 8 is a front elevation lookin into the mouth of the projector shown in Figures 6 and 7.

In Figure 1 the various parts of a cabinet phonograph are conventionally indicated. The case 1, has a cover 2, enclosing a shallow cavity 3, having a bottom 4, sup porting the phonograph motor case 5, the rotary support 6 for the record, the tone' arm swivel 8 and tone arm 9,'all of which may be of any known or desired construction.

The reproducer 10 preferably has the low frequency characteristics referred to above and more fully explained in my prior applications, the stylus lever being rigid, the mounting and tensioning devices therefor having slight resilient effect as against. oscillatory movement of the lever and thediaphragm being comparatively large and flexible. Any other construction adapted to afford the desired low frequency characteristics for the reproducer, may be employed.

Communicating with the lower end of the tone arm is the upper end 11 of the tubular conduit 12 leadmg to the reflecting projector. This conduit has the form of a frustrum of a pyramid curved rearwardlv and diverging laterally so that at the lower end, where it joins the reflecting projector, it is only a little less than the full width of the latter. This expansion passage is preferably of gray cast iron with its walls about inch thick so that, acoustically considered, it forms a natural extension of the sound conducting passage 'ali'orded by the tone arm 9.

The sound waves which are propagated from the lower end of conduit 11, impinge downward l u on the sonorous reflect" 0 plate 13 at a high angle. As shown, this angle is 45 for most of the'wave front though somewhat less than thisfor the part that spreads from the lower flank of the sound {Thec'onstruction and mounting of this reflecting plate 13 is indicated in the various figures but is shown more clearly in Figures'4 and 5. The mounting comprises the very substantially ri "d frame which may wide by half an inch thick, or if of -metal, may be of less cross section. The side faces at 21, 21 areprefeia abl smoothly finished so as. to lie in exact y the same plane. To these faces are secured the sensitiveplate 13, by screws-22' arranged at short intervals. The heads of these screws preferably have flat under sat-- faces to engage squarely with the top sur faceof plate '13, so as to clamp the same as -'ri gidly as po ible. The two other side members of the frame are recessed at 23 so q as to give a clearance for the adjacent free edges of the vibratory plate 13. The recesspreferably as shallow as the purpose permit, of an inch bein usually sufficient. In assembling the re ecting plates fi iifiththe other members of the pro ector, a is taken to secure. a ri 'd clamping contact applying symmetrica pressure to theglate 13 at exactly corresponding points 7 "precaution is very important ascontributmg to proper. reaction of the plates with ref- .eren'ce to the waves impinging thereon.

In assembling the plates in the projector,

it is important to arrange the clamped edges ofthe" lates at the si es of the projector to ave the free edges extending trans where two y lower right and cornerm vigure 1, 1t is de- :the free edge of t e adjacent versely. As indicated in'Figure .1, the as-' 'smbly. is such as. to leave the unclamped "edges of the plates free of any possible vibratofy contact with adjacent elements and lates come to other as at the sirable to have one late as 13 extended past late. The uniform spacing of plate 13 is 0 early indicated'at 18, Figure 1.

4 the waves reflected therefrom at a 45 angle to spread spherically in all directions.

e upper and lower surfaces thereof, as shown'at 24, 25, Figure 5. I find that-thisimpinge upon a second reflector 14 whence they are reflected upward and out of the projector at'a 45 angle.

Afterthe second or final reflection of the sound beam from the bottom plate 14, it

travels approximately parallel with a third sound sensitive plate 15 which serves to hold the upper flank of the beam from lateral diffusion while the lower flank thereof is free to diffuse toward horizontal and downward 7 directions by following its natural tendency This seems to give the best possible distribution for listeners in an ordinary room when the mouth of the projector is at the usual level of three to four feet from the floor.

It will be understood that the sound beam is subject to spherical diffusion 'wherever its lateral flanks are not guided and confined and that such diffusion tends to occur inside of the projector as well as outside but suchflank diffusion is proportional to the density of the compressions and rare fications in the individual waves, and this density is enormously decreased by the expansion effected in the passage 12 which may have an area of say three square inches, at the upper end expanding to say twenty square inches at the lower end. Morcver,

the main reflections are only two in numher, and the exposed flanks are short so that opportunities for objectionable diffusion effects are minimized and such diffusion as there is has a fairly direct path outward through the mouth of the horn. This fact is evidenced in practice by the remarkable clearness and vividness of quality of the projected Sound.

As explained in my prior applications, the

reflecting plates are preferably of such quality and thinness that they will causeresonant reinforcement of the sound and will vibrate 'responsively thereto. Any vibrations thus set up in the plates cause them to be sources of re-radiated energy propagated at right angles to the surface of the plate. Any such waves generated by plate 13 are mostly propagated directly out of the mouth of the projector. Similar waves re-radiated from 14 will mostly impinge 'upon reflector 15 and be reflected out of the projector along lines parallel with the radiation from plate 13.

During propagation through the reflecting projector, the sound waves are permitted to expand laterally at a rate somewhat more rapid thanin the expansion passage 12, the

divergence of the side walls 16 of the prov jectorxbeing nearly an inch laterally for each inch measured along the axis of the projector, as may be seen by reference to Thus the expansion is 1 Figures 2 and 3. progressive from the point where the waves enter the expanding passage at 11 to the mouth of the projector where they emerge 1 the open'air.

, inches.

The above described parts are organized so as to afford the above described gradw ated expansion of the wave front and application thereof to the outside air over a large area, combined with adesircd minimum for the distance of travel of the waves during such expansion. To this end, the tone arm is pivoted at the front of the cabinet almost directly over the outlet instead of being pivoted in the rear as is now common practice in commercial devices of this type. This makes it desirable to slant thereproducer stylus toward the pivotal point of the tone arm instead of away from it because this arrangement permits the operator to use his right hand for manipulation of the box to pivot it to and from the record and to renew the stylus needles.

By this location of the tone arm, the length required for the reflecting projector is reduced to about half that shown in my prior applications. In this connection, it is to be remembered that physical dimensions as well as'proportions are of considerable importance where amplifying and resonance effects are to be produced on sound waves, because the functioning of such devices are intimately related with the physi cal lengths of the waves to be amplified thereby. Hence, while very wide latitude is permissible, some notion ofdesirable sizes is necessary. In my preferred apparatus, the rear sensitive plate 13 may be nearly square or say 8v inches high by 7 inches wide, the sound beam projected thereon being of slightly less width say 6 inches by 3 The bottom plate 14 will be of the same width at the rear as plate 13; will he say 8 or 9 inches from rear to front, and will be about 15 or 16 inches wide, at the front. The dimensions of plate 16 will be those required for a 45 plate to fit the dimensions previously given, and the vertical height of the outlet opening determined thereby may be say 9 or 10 inches.

- The amplifying rojector is thus only about 8 or 9 inches eep from front to rear. This is the physical length of a quarter wave of a note of about 350 frequency. It is also the three-quarter length of the wave of a note of somewhat over 1000 frequency. Hence, while the proportions and shape of this cavity are not such as to promote very sharp air column resonance for any frequency, and while the wide mouth tends to make the air cavity more or less omnipe riodic, it is important to note that the periodicities which it ought to reinforce most strongly include substantially the entire range of important s eech frequencies. Moreover, for such rein orcement, the stationary air waves established by reflection from the mouth of the projector back to the rear wall 13, will never have to be over three-quarters of a wave for the higher frequencies, and for certain of the important lower frequencies will be only one-quarter of a wave.

If the projector be somewhat deeper than this, say 12 inches from front to rear as is sometimes desirable where thelateral flare of the walls is not so extreme, its character istics so far as concerns quarter wave length, will extend down to and include frequencies of say 27 5 to 250, without lowering the three-quarter wave length situation below the frequencies lying between 900 and 1000 and hence not below the uppermost of the vowel sounds. Any pronounced air column resonance for frequencies lower than 250 or even 350 is sulficient since the lower frequencies are not so subject to attenuation as the higher ones and they are sufficiently preserved and amplified by the sounding board effect of the wallsof the projector.

While I do not wish to. be considered a limiting my invention or making it in any wise depending upon the correctness of th theories above advanced, it is evident that they seem to fit the facts; that they tend to account for the remarkable results achieved and that they afford an intelligent basis to work from in practicing my invention and in devising desirable modifications'thereof.

Another feature of my invention which apparently contributes to the new results attained, is the employment of rolled sheet aluminum for the plates. These are preferably about 16 to 22 gauge. Such plates, though relatively thick and stiff, seem to be flexible enough and sensitive enough when clamped at the side edges only.' They seem to be of advantage for my present purpose because theyapparently reflect a large percentage of the energy and such part of the energy as is expended in causing resonant vibration of the plates is re-radiated with very small loss due to the dense nature of the material of the plates and the small internal friction. They seem not to use up and dissipate energy to anything like the extent that thin wooden plates do, even when the latter are of most carefully selected and finished material. 7

Figures 6, 7 and 8 show the projector substantially as described above but having the added feature of diverging partition plates 'lt), 19 arranged opposite to and preferably parallel with the side walls 16. These plates are held in position b transverse rods 30, 31 secured through t e wide walls by clamping nuts 32. T e partition members are threaded on these rods and are secured in position by clamping nuts 33, 33. It will be noted that these partition members extend rearward about half the depth of the reflecting projector and are supported by the rods 30, 31 in position to barely clear the sensitive reflecting plates 14, 15.

Preferably the partition plates are sensitive plates of the same kind and. mounting as above described for plates 13, 14? and 15. The clamped edges being arranged at. top and bottom and the free vibratory edges transverse to the direction of'propagation ofthe waves. I claim:

1. A sound amplifier including a primary expansion conduit having an oblong outlet,-

lng wall at an angle of approximately 45 degrees to said outlet, a second reflecting and a projector portion comprising reflectr'wall immediately adjacent and approximately at right angles to the first and extending approximately to theeXit plane or mouth of said projector portion, and a all opposite said second reflector, approximately paral- 1 lel 'With and out of the path of the main sound beam reflected from said second refiector.

other on the same side of the device, one

reflector being in receiving relation to the beam from said primary conduit and the second reflector being in receiving relation to the first and extending approximately to the exit plane of the mouth of said projector so that the main beam from the second reflector is projected directly across said plane into the'outer air.

' Signed at New York city in the county of New York and State of New York this tenth day of May A. D. 1920.

ELWOOD GRISSINGER. 

